1. Fitzwilliam College, University of Cambridge, Cambridge CB3 0DG, UK (cc2006@cam.ac.uk)
2. Faculty of Medicine, University of Manitoba, 750 Bannatyne Ave., Winnipeg, MB R3E 0W3 (evelyn.forget@med.umanitoba.ca)
3. Department of Economics, University of Rochester, 280 Hutchinson Road, Box 270156, Rochester, NY 14627 (john.singleton@rochester.edu)